1. Field of the Invention
The present invention relates to a radiation-sensitive resin composition and, more particularly, to a radiation-sensitive resin composition suitable as a chemically-amplified resist useful for microfabrication utilizing various types of radiation, for example, deep ultraviolet rays such as a KrF excimer laser or ArF excimer laser, X-rays such as synchrotron radiation, or charged particle rays such as electron beams.
2. Description of the Background Art
In the field of microfabrication represented by fabrication of integrated circuit devices, a lithographic technology enabling microfabrication with a line width of 0.20 xcexcm or less has been demanded in order to achieve higher integration.
A conventional lithographic process utilizes near ultraviolet rays such as i-line as radiation. It is known in the art that microfabrication with a line width of sub-quarter micron is very difficult using near ultraviolet rays.
Therefore, use of radiation with a shorter wavelength has been studied for enabling microfabrication with a line width of 0.20 xcexcm or less. As radiation with a shorter wavelength, deep ultraviolet rays represented by a line spectrum of a mercury lamp and an excimer laser, X-rays, electron beams, and the like can be given. Of these, a KrF excimer laser (wavelength: 248 nm) and an ArF excimer laser (wavelength: 193 nm) have attracted attention.
As a radiation-sensitive resin composition applicable to the excimer laser radiation, a number of compositions utilizing a chemical amplification effect between a component having an acid-labile functional group and a component generating an acid (hereinafter called xe2x80x9cphotoacid generatorxe2x80x9d) which generates an acid upon irradiation (hereinafter called xe2x80x9cexposurexe2x80x9d) has been proposed. Such a composition is hereinafter called a chemically-amplified radiation-sensitive composition.
As the chemically-amplified radiation-sensitive composition, Japanese Patent Publication No. 27660/1990 discloses a composition comprising a polymer containing a t-butyl ester group of carboxylic acid or a t-butylcarbonate group of phenol and a photoacid generator. This composition utilizes the effect of the polymer to release a t-butyl ester group or t-butyl carbonate group by the action of an acid generated upon exposure to form an acidic group such as a carboxylic group or a phenolic hydroxyl group, which renders an exposed area on a resist film readily soluble in an alkaline developer.
Most of conventional chemically-amplified radiation-sensitive compositions use a phenol resin as a base resin. Deep ultraviolet rays used as radiation for exposure are absorbed due to an aromatic ring in the resin and cannot sufficiently reach the bottom of the resist film. Because of this, the dose of the radiation is greater at the film surface and is smaller at the bottom of the resist film. This causes critical dimension of a resist pattern to be smaller at the film surface and be larger toward the bottom, thereby forming a tapered profile after development. No sufficient resolution can be obtained from such a resist film. Such a tapered profile formed after development cannot give a desired dimensional accuracy in the succeeding steps such as an etching step and an ion implantation step. In addition, if the configuration of the resist pattern is not rectangular on the upper portion, the resist disappears faster during dry etching, making it difficult to control etching conditions.
The resist profile can be improved by increasing the radiation transmittance through the resist film. For example, (meth)acrylate resins represented by polymethylmethacrylate are desirable from the viewpoint of radiation transmittance due to the superior transparency to deep ultraviolet rays. Japanese Patent Application Laid-open No. 226461/1992 proposes a chemically-amplified radiation-sensitive resin composition using a methacrylate resin. However, in spite of the excellent micro-processing performance, this composition exhibits only poor dry etching resistance due to the absence of an aromatic ring, giving rise to difficulty in performing etching with high accuracy. This composition thus does not have both radiation transmittance and dry etching resistance at the same time.
A method of introducing an alicyclic ring into the resin component in the composition instead of an aromatic ring has been known as a means for improving dry etching resistance without impairing radiation transmittance of the resist made from a chemically-amplified radiation-sensitive resin composition. A chemically-amplified radiation-sensitive resin composition using a (meth)acrylate resin having an alicyclic ring is proposed in Japanese Patent Application Laid-open No. 234511/1995, for example.
This composition, however, comprises groups which are comparatively easily dissociated with conventional acids (for example, an acetal functional group such as a tetrahydropyranyl group) and groups which are comparatively difficult to be dissociated with acids (for example, a t-butyl functional group such as a t-butyl ester group, t-butylcarbonate group) as an acid-labile functional group as the resin component. The resin component possessing the former acid-labile functional group exhibits excellent basic characteristics as a resist such as superior sensitivity and excellent pattern shape, but has a problem of poor storage stability, whereas the resin component possessing the latter acid-labile functional group exhibits impaired resist characteristics, particularly in terms of sensitivity and pattern shape, in spite of excellent storage stability. In addition, inclusion of an alicyclic structure in the resin components of this composition increases hydrophobicity of the resin, resulting in poor adhesion to substrates.
In view of recent progress in the microfabrication of semiconductor devices, development of a novel resin component exhibiting high transmittance of radiation, having excellent basic properties as a resist, and suitable for use in chemically amplified radiation sensitive compositions which can be adapted to short wavelength radiation represented by a deep ultraviolet rays is an important subject.
Therefore, an object of the present invention is to provide a novel radiation-sensitive resin composition, which has high transmittance of radiation, exhibits superior basic properties as a resist such as high sensitivity, resolution, and pattern shape, and is capable of producing semiconductors at a high yield without producing resolution defects during microfabrication.
The above object can be achieved in the present invention by a radiation-sensitive resin composition comprising (A) an acid-labile group-containing resin having a structure represented by the following formula (1) and (B) a photoacid generator: 
wherein R1 represents a hydrogen atom, a monovalent acid-labile group, an alkyl group having 1-6 carbon atoms which does not have an acid-labile group, or an alkylcarbonyl group having 2-7 carbon atoms which does not have an acid-labile group, X1 represents a linear or branched fluorinated alkyl group having 1-4 carbon atoms, and R2 represents a hydrogen atom, a linear or branched alkyl group having 1-10 carbon atoms, or a linear or branched fluorinated alkyl group having 1-10 carbon atoms.
In a preferred embodiment of the present invention, the above component (A) is an acid-labile group-containing resin having a recurring unit (I) represented by the following formula (2): 
wherein R1 represents a hydrogen atom, a monovalent acid-labile group, an alkyl group having 1-6 carbon atoms which does not have an acid-labile group, or an alkylcarbonyl group having 2-7 carbon atoms which does not have an acid-labile group, X1 represents a linear or branched fluorinated alkyl group having 1-4 carbon atoms, R2 represents a hydrogen atom, a linear or branched alkyl group having 1-10 carbon atoms, or a linear or branched fluorinated alkyl group having 1-10 carbon atoms, R3, R4, and R5 individually represents a hydrogen atom or a linear or branched alkyl group having 1-4 carbon atoms, a monovalent oxygen-containing polar group, or a monovalent nitrogen-containing polar group, n is an integer of 0-2, and m is an integer of 0-3.
In another preferred embodiment of the above radiation-sensitive resin composition the above component (A) is an alkali insoluble or scarcely soluble acid-labile group-containing resin having a recurring unit (I) and a recurring unit (II) shown by the following formula (3): 
wherein R1 represents a hydrogen atom, a monovalent acid-labile group, an alkyl group having 1-6 carbon atoms which does not have an acid-labile group, or an alkylcarbonyl group having 2-7 carbon atoms which does not have an acid-labile group, X1 represents a linear or branched fluorinated alkyl group having 1-4 carbon atoms, R2 represents a hydrogen atom, a linear or branched alkyl group having 1-10 carbon atoms, or a linear or branched fluorinated alkyl group having 1-10 carbon atoms, R3, R4, and R5 individually represents a hydrogen atom or a linear or branched alkyl group having 1-4 carbon atoms, a monovalent oxygen-containing polar group, or a monovalent nitrogen-containing polar group, n is an integer of 0-2, and m is an integer of 0-3.
In the above radiation-sensitive resin composition, the content of the recurring unit (I) in the resin component (A) is preferably 1-50 mol % of the total amount of recurring units.
In the above radiation-sensitive resin composition, the alkali insoluble or scarcely soluble acid-labile group-containing resin (A) has a recurring unit (I), recurring unit (II), and recurring unit (III) shown by the following formula (4): 
wherein R1 represents a hydrogen atomn, a monovalent acid-labile group, an alkyl group having 1-6 carbon atoms which does not have an acid-labile group, or an alkylcarbonyl group having 2-7 carbon atoms which does not have an acid-labile group, X1 represents a linear or branched fluorinated alkyl group having 1-4 carbon atoms, R2 represents a hydrogen atom, a linear or branched alkyl group having 1-10 carbon atoms, or a linear or branched fluorinated alkyl group having 1-10 carbon atoms, R3, R4, and R5 individually represents a hydrogen atom or a linear or branched alkyl group having 1-4 carbon atoms, a monovalent oxygen-containing polar group, or a monovalent nitrogen-containing polar group, n is an integer of 0-2, m is an integer of 0-3, R6 represents a hydrogen atom or methyl group, and R7 individually represents a linear or branched alkyl group having 1-4 carbon atoms or a monovalent alicyclic hydrocarbon group having 4-20 carbon atoms or a derivative thereof, or any two of R7s form in combination a divalent alicyclic hydrocarbon group having 4-20 carbon atoms or a derivative thereof, with the remaining R7 being a linear or branched alkyl group having 1-4 carbon atoms or a monovalent alicyclic hydrocarbon group having 4-20 carbon atoms or a derivative thereof.
In the above radiation-sensitive resin composition, the component (A) is an acid-labile group-containing resin having a recurring unit (IV) represented by the following formula (5): 
wherein R1 represents a hydrogen atom, a monovalent acid-labile group, an alkyl group having 1-6 carbon atoms which does not have an acid-labile group, or an alkylcarbonyl group having 2-7 carbon atoms which does not have an acid-labile group, X1 represents a linear or branched fluorinated alkyl group having 1-4 carbon atoms, R2 represents a hydrogen atom, a linear or branched alkyl group having 1-10 carbon atoms, or a linear or branched fluorinated alkyl group having 1-10 carbon atoms, R8, R9, and R10 individually represents a hydrogen atom or a linear or branched alkyl group having 1-4 carbon atoms, a monovalent oxygen-containing polar group, or a monovalent nitrogen-containing polar group, n is an integer of 0-2, and m is an integer of 0-3.
In the above radiation-sensitive resin composition, the photoacid generator of component (B) is at least one compound selected from the group consisting of an onium salt compound, halogen-containing compound, diazoketone compound, sulfone compound, and sulfonic acid compound.
The above radiation-sensitive resin composition preferably further comprises a nitrogen-containing organic compound as an acid diffusion controller.
The above radiation-sensitive resin composition preferably further comprises an alicyclic additive having an acid-labile organic group.
The above alicyclic additive is preferably at least one compound selected from the group consisting of an adamantane derivative, a deoxycholate, a lithocholate, and 2,5-dimethyl-2,5-di(adamantylcarbonyloxy)hexane.
Other objects, features and advantages of the invention will hereinafter become more readily apparent from the following description.